1) Field of the Invention
The present invention relates to a heating unit and a fixing unit that include a heating member that produces heat with charging of a capacitor, an auxiliary power unit and a fixing unit that include a plurality of capacitors serially connected to each other, and an image forming apparatus including the above fixing unit.
2) Description of the Related Art
Japanese Patent Application Laid Open No. 2000-315567, Japanese Patent Application Laid Open No. 2002-357966, and Japanese Patent Application Laid Open No. 2003-140484 disclose technologies for a heating member (fixing heater) of a fixing unit used in an electrophotographic image forming apparatus. This technology is such that in addition to a power supply from a commercial power supply, a chargeable auxiliary power supply that uses an electric double layer capacitor is used to allow fast rising of temperature and enhance effects of power saving.
Electrophotographic image forming apparatuses and other electronic devices including a power saving mode are known. In the power saving mode, when the electrophotographic image forming apparatus or the like is in a standby state and is not used for a fixed time, a power supply to power loads thereof is restricted and the power is supplied only to some circuits minimum required to allow power saving and energy saving. One of these is disclosed in Japanese Patent Application Laid Open No. 2002-304088.
In the electrophotographic image forming apparatus, if temperature of a fixing unit is made to rise quickly by the chargeable auxiliary power supply using the capacitor such as the electric double layer capacitor, the power of the capacitor if it is low cannot increase the fixing temperature quickly. Therefore, when the charging power of the capacitor decreases to a predetermined level or less, a specified controller needs to control a charger so as to charge the capacitor.
However, in such an image forming apparatus as explained above that includes the power saving mode, if a power supply to the controller (e.g. microcomputer) that controls the charger so as to charge the capacitor is also stopped when mode shifts to the power saving mode, the capacitor is not charged in the power saving mode. In this case, if the amount of charge in the capacitor decreases to a quite low level right before shifting to the power saving mode, or if the power saving mode is active for a long time and natural discharge of the capacitor occurs, the charge amount of the capacitor is insufficient by the time it is returned from the power saving mode, which makes it impossible to quickly increase the fixing temperature of the fixing unit.
In such a case, it is possible to rapidly increase the fixing temperature by maintaining the power supply to the controller even after the shift to the power saving mode. However, the controller also consumes power even in the power saving mode, which is quite difficult to achieve satisfactory power saving and energy saving.
In the technologies disclosed in Japanese Patent Application Laid Open No. 2000-315567, Japanese Patent Application Laid Open No. 2002-357966, and Japanese Patent Application Laid Open No. 2003-140484, by using the capacitor including the electric double layer capacitor (large capacitor) as an auxiliary power supply, degradation of fixability due to power failure can be prevented. That is because a large amount of current can be instantly supplied from the capacitor to the fixing unit when the power supply to the fixing unit from the commercial power supply is insufficient. However, the technologies have such inconvenience that the capacitor has to be charged at a predetermined timing after the capacitor discharges to supply power to the heating member. Moreover, since a large amount of power has to be supplied from the commercial power supply during the charging, a copying operation cannot concurrently be executed by a copying machine, which causes a down time to occur in the copying machine and the operability of a user to be reduced.